1. Field of the Invention
The invention relates to displays, and more particularly, to methods and apparatus for reducing unwanted reflections in displays.
2. Description of the Related Art
In display applications, it is difficult to maintain high contrast output at high ambient illumination levels. However, polarized light displays and active matrix liquid crystal display (AMLCD) flat panels work well in maintaining the contrast in their displays because light passes through several absorbing layers before reflecting or scattering back out from the light producing mechanism. The multiple layers, however, adversely affect the total reflectance of the display. Even though the reflectance at layer boundary in itself may be quite small, the sum of the reflections may be significant.
Referring to FIG. 1, a conventional polarized display 2, such as a liquid crystal display (LCD), includes a cover glass 4 having an antireflective coating 6. A front polarizer 8, a first substrate 10, a liquid crystal layer 12, a second substrate 14, and a rear polarizer 16 are sandwiched between the cover glass 4 and a backlight 18. The cover glass 4 is separated from the front polarizer 8 by a gap 9, typically filled with air. The reflectance at each boundary between the layers adds to the overall reflectance of the display. Reflectances associated with the boundaries between the cover glass 4, the gap 9, and the front polarizer 8 are especially pronounced.
Several methods have been developed to reduce reflectances. For example, antireflection coatings 6 may be added to one or both sides of the cover glass 4, which tends to reduce the reflection from the front of the cover glass 4. Additionally, an antireflection coating may be added to the surface of the front polarizer 8. However, the suppression of the residual reflection still remains a problem. Another method involves applying adhesives between the cover glass 4 and the front polarizer 8 to bond the glass to the polarizer and achieve some level of index matching, which tends to reduce the reflectances from the boundary between the cover glass 4 and the air gap 9 or the front polarizer 8. While bonding the cover glass 4 to the display is somewhat successful in reducing reflectances, it tends to affect the uniformity of the liquid crystal cell gap, induces difficulty in repairs, and is associated with other problems due to aging effects and shrinkage of the adhesive.
Another alternative is to add attenuating contrast enhancement filters to the display to filter out the reflectances. For example, a filter may be added between the cover glass 4 and the gap 9 or the front polarizer 8, or alternatively a specialized tinted glass may be used for the cover glass 4. Addition of the filter reduces reflection, but also attenuates the display output. Further, addition of the filter tends to promote other issues, such as cost, color shifts, and environmental concerns.
A display according to various aspects of the present invention comprises a polarized display that has reduced reflectances in the output of the display to maintain high contrast output, high illumination levels, and less expensive production. A polarizer is disposed adjacent to a cover glass in front of the display. Light intended to be transmitted through the display is transmitted by the polarizer. Light reflected after passing through the polarizer is further attenuated as it intercepts the polarizer following reflection.